Effective Availability Calculation

Effective Availability

EA Calculation

Effective Availability is calculated for each aggregator system as follows:

$$Ea\%\ =\ \frac{Energy\ Produced}{Energy\ Produced\ +\ Energy\ Lost}$$

It is calculated on a granular level (depending on the readout frequency, i.e. for every 5 or 15 minute period). The daily EA is calculated the same way but of course the values are for the whole day. The daily Energy Produced and Energy Lost values are determined by summing the values calculated on the granular level for the given day.

EA is only calculated "when the sun is shining", which means that if the site is not expected to be producing, then EA is not calculated at all for that 5 or 15 minute period. Irradiance as well as the current average power production of all subsystems are used to determine whether all subsystem of a given system are expected to be producing. This is necessary since we don't expect units to produce in the dark.

The exact algorithm to determine whether a system is expected to be producing is as follows:

If an irradiance threshold is not set for the site, or irradiance is unavailable, 
	and the sum of the average power of all subsystems during the previous period exceeds the minimum power threshold
	→ then all subsystems are expected to be producing
Otherwise, if irradiance threshold is set for the site 
	and irradiance readouts are available 
    and the current measured irradiance exceeds the irradiance threshold
	→ then all subsystems are expected to be producing
   → the site is not expected to be producing (no EA is calculated)

The Minimum Power Threshold is determined as 1% of the sum of module outputs for the given system.

The Irradiance Threshold can be set on the site configuration form for the whole site:

Energy Produced is calculated simply as the sum of the readouts of all subsystems. 

Energy Lost is calculated based on the energy produced by units (which we call subsystems) that are online, if available:

$$Energy\ Lost\ =\ Energy\ Produced\ *\ \frac{DC\ Size\ of\ Units\ Offline\ +\ DC\ Size\ of\ Units\ Not\ Producing}{DC\ Size\ of\ Online\ Subsystems}$$

DC size of units is determined from the Module Output of the system, which in turn is the sum Wattage * Device Count of all "Module" type devices registered to that system. In case of virtual aggregator systems, this value is calculated from its subsystems that do have modules.

A subsystem is considered online in the context of the above equation if it produced at least 0.5 kW over the preceding period at an average power of at least 0.1% of the rated module output.

A subsystem is considered not producing if it is reporting values, but these values are below the threshold explained above.

A subsystem is considered offline if readings are unavailable.

If no subsystems are online, then we use the predicted hourly output for the aggregator system to calculate the energy lost. The predicted hourly output for an aggregator system is calculated as follows:

$$\frac{System\ Size\ *\ Derate\ Factor\ *\ Irradiance}{1000} \ *\ ( 1-Temp.\ Coefficient\ *\ ( Celsius\ Cell\ Temp.-25))$$

We can then get the energy lost as follows:

$$Energy\ Lost\ =\ \frac{Predicted\ Hourly\ Energy\ Output}{60} \ *\ Minutes\ in\ Period$$

EA Visualization

The EA for each site is available from the Analytics tab on the site details page:

The values are also available in a table on the Local Readings tab for each site:

The result includes the values used in the calculation, and can be exported in various formats:

Use the Local Readings tab to drill-down and identify why the site underperformed on a given day (circled in the previous image):

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